1. Field of the Invention
The present invention relates to a backlight assembly and a display device using the same, and more particularly, to a backlight assembly for a thin portable liquid crystal display (LCD) device, which is capable of selectively lighting up different screen areas of the portable LCD device without increasing the thickness of the portable LCD device.
2. Discussion of the Related Art
With rapid development of information technology, flat panel display devices are in great demand because of their superior characteristics such as thin profile, light weight, and low power consumption. Among those flat panel display devices, liquid crystal display (LCD) devices having excellent color reproduction are being aggressively researched and developed.
The LCD device includes an LCD panel having a thin film transistor (TFT) substrate, a color filter substrate and a liquid crystal layer disposed therebetween. Since the LCD panel does not emit light by itself, the LCD device includes a backlight assembly at a rear side of the LCD panel as a light source for providing light. The transmittance of the light generated from the backlight assembly is adjusted according to an alignment of the liquid crystal layer. The LCD panel and the backlight assembly are accommodated in a chassis of the LCD device. Depending on a location of the light source, the backlight assembly may be classified as an edge-type or direct-type backlight assembly. The edge-type backlight assembly is provided with a light source at a lateral side of a light guiding plate and is typically used for relatively small sized LCDs. The edge-type backlight assembly provides high light uniformity and good endurance and is suitable for use in thin profile LCDs, such as lap tops, portable TVs and DVD players.
Hereinafter, an LCD device with a backlight assembly according to the related art will be described with reference to FIGS. 1 and 2. FIG. 1 is a view schematically illustrating a related art LCD device 1, and FIG. 2 schematically illustrates a vertical section of the related art LCD device 1 of FIG. 1. Referring to FIGS. 1 and 2, the related art LCD device 1 includes an LCD panel 10, a light filter layer 20 arranged behind the LCD panel 10, a light guide plate 30 arranged behind the light filter layer 20, and a light source 40 arranged laterally at the side of the light guide plate 30. The light guide plate 30 may have a thickness usually from 2 mm to more than 10 mm. The light guide plate 30 may be made of a transparent plastic material. The light source 40 may include one or a plurality of lamps.
As shown in FIG. 2, there are a plurality of diffusion lines or surfaces 50 painted on a rear surface of the light guide plate 30. These diffusion lines or surfaces 50 serve to diffuse light, which is emitted from the light source 40 and then guided by the light pipes of the light guide plate 30. When the light source 40 turns ON to emit light beams 60 through the edge of the light guide plate 30, the light beams 60 bounce inside the light guide plate 30 until they hit the diffusion lines or surfaces 50 painted on the rear surface of the light guide plate 30. Some of the diffused light beams 60 will go through a front surface of the light guide plate 30 to be guided toward the LCD panel 10, when the angles between the light beams 60 and the perpendicular of the front surface are small enough. Moreover, the reference numeral 70 denotes that the light beams 60 make specular reflection inside the light guide plate 30.
The LCD panel 10 includes a plurality of the pixels (not shown) arranged in a matrix of rows (lines) and columns. The pixels are “refreshed” line by line. Since changing a pixel state from ON to OFF takes time, if the back light is ON at all times, it can cause some undesirable picture artifacts. For this reason, it would be good to turn off the light in the area of the screen of the LCD panel 10, in which the pixels are being “refreshed”.
It is also possible to create a software program in a TV using the LCD panel 10, which analyzes the image to decide if all areas of the picture need full brightness or if the back light for some areas can be turned off. This can be an energy saving feature for the TV, but it means that some lamps of the light source can be turned off independently of the other lamps.
In the direct-type backlight assembly, a light source is arranged right behind a screen of the LCD panel, and therefore can be designed and controlled to light up different parts of the screen of the LCD panel independently. However, this manner of mounting the light source in the direct-type backlight assembly may objectively increase the thickness of the LCD device, which is not desirable for portable LCD devices, such as lap tops, portable TVs, and the like. On the other hand, the related art LCD device using the edge-type backlight assembly cannot selectively illuminate areas of the screen of the LCD device.